The management of solid wastes such as municipal wastes from residential, institutional, and commercial sources, agricultural wastes, and other wastes such as sewage sludge, remains a challenging issue with ever-evolving solutions. As landfills reach and exceed capacity worldwide, and as the solid waste industry and societies generally limit the use of landfills, alternative methods of managing solid wastes and have been developed that additionally process the solid wastes to reduce the volume introduced into landfills. Recycling of metals, plastics, and paper products, as well as composting organic matter are relatively common methods of reducing the overall volume of solid wastes going to landfills. Waste-to-Energy processes have also been developed to convert the energetic content of solid wastes into a more usable form such as electrical power.
A variety of Waste-to-Energy processes may use thermal treatments such as incineration, pyrolysis, or gasification to release the energy content of the solid waste stream, which is subsequently used to drive downstream electrical generators. Although pyrolysis and gasification afford many advantages over incineration in Waste-to-Energy processes, the effective use of pyrolysis or gasification is limited when municipal solid waste (MSW) or agricultural waste is used as the feedstock, due to the high water content, low density, and lack of homogeneity.
Efficient operation of a pyrolysis or a gasification chamber typically uses feedstock that is high density and of consistent composition with essentially no moisture. Because solid waste streams are inherently low density and variable in composition, most Waste-to-Energy plants incinerate the solid waste stream to liberate the energy of the solid waste stream. Enhanced pyrolysis mechanisms, such as advanced gasification, may overcome inefficiencies associated with the inherent inconsistency of solid waste composition, but these advanced mechanisms require significant investment in specialized equipment. Further, they are still limited by the quality of the feedstock.
Other processes use pelletizers to render the solid waste stream of the pyrolysis chamber more uniform in size. But the pelletized solid waste retains the variation in composition inherent in solid waste streams. Further, pelletizing the solid waste stream fails to transform the solid waste into a high density and low moisture fuel appropriate for the efficient operation of a pyrolysis (or gasification) chamber.
A need exists for a solid fuel composition and a process of producing a solid fuel composition from a solid waste stream that may include mixed solid wastes and other wastes to be used as a feedstock. Such a fuel would provide efficient operation of a pyrolysis (or gasification) chamber as part of a Waste-to-Energy process, without additional capital investment in advanced machinery. In addition, a need exists for a process that transforms a solid waste stream with variable composition into a solid fuel composition with a relatively consistent composition that is high density and low moisture, as this provides a better fuel composition. Further, a need exists for a process for forming a solid fuel composition from a solid waste stream that may further eliminate odors, bacteria, and other undesired properties of the solid waste stream used to produce the solid fuel composition. The solid fuel composition resulting from such a process may enable the use of high-efficiency pyrolysis or gasification methods as part of a Waste-to-Energy process by providing a homogenized, dry, dense, and energy rich fuel primed for pyrolysis or gasification.